Electric furnace and method for the continuous refining of magnesium

ABSTRACT

An electric furnace for the continuous refining of magnesium, comprising an interior subdivided by vertical partitions into a central chamber and peripheral chambers surrounding it. The furnace bottom has a recess in its central portion in the form of a basin. The partitions forming the peripheral chambers are fitted with openings through which magnesium overflows from the first in the direction of the process flow chamber into another. The central chamber is adapted for the centralized removal of slime from all the chambers, communicating therewith in their bottom portion, its upper opening being closed with a cover. Such a furnace is more dependable in service, has a higher production rate and ensures favorable working conditions.

United States Patent 1191 Kosarev et al.

[ May 6,1975

ELECTRIC FURNACE AND METHOD FOR THE CONTINUOUS REFINING OF MAGNESIUM Inventors: Sergei Petrovich Kosarev,

Nalichnaya ulitsa, 39, korpus 1, kv. 20; Nina Voldemarovna Didrikh, Moskovsky prospekt 220, kv. 26, both of Leningrad; Vladimir Dmitrievich Yazev, ulitsa Bogdana Khmelnitskogo, 66, kv. 59, Kalush lvano-Frankovskoi oblasti; Viktor Georgievich Raskatov, ulitsa Khimikov, l4, kv. 8, Kalush lvano-Frankovskoi oblasti; Oleg Nikolaevich Romanenko, ulitsa Sevastopolskaya, 96, kv. 46, Kalush lvano-Frankovskoi oblasti; Alexandr Fedorovich Trukliin, ulitsa Zhdanova, 11, kv. 32, Kalush lvano-Frankovskoi oblasti, all of U.S.S.R.

Filed: May 2, 1974 Appl. No.: 466,493

[56] References Cited UNITED STATES PATENTS 1,930,337 10/1933 Blomberg 7. 13/23 S 3,666,870 5/1972 Kemper 13/23 Primary Examiner-R. N. Envall, Jr. Attorney, Agent, or Firm-Lilling & Siegel [57] ABSTRACT An electric furnace for the continuous refining of magnesium, comprising an interior subdivided by vertical partitions into a central chamber and peripheral chambers surrounding it. The furnace bottom has a recess in its central portion in the form of a basin. The partitions forming the peripheral chambers are fitted with openings through which magnesium overflows from the first in the direction of the process flow chamber into another. The central chamber is adapted for the centralized removal of slime from all the chambers, communicating therewith in their bottom portion, its upper opening being closed with a cover.

Such a furnace is more dependable in service, has a higher production rate and ensures favorable working conditions.

14 Claims, 5 Drawing Figures PATENTEDHAY ems 3 882 261 sum 10? 2 PAII'ENTEBMAY'BISYS 3,882,261

SHEET E0? 2 ELECTRIC FURNACE AND METHOD FOR THE CONTINUOUS REFINING OF MAGNESIUM BACKGROUND OF THE INVENTION The present invention relates to electric furnaces for the continuous refining of magnesium utilized at metallurgical enterprises.

The process of refining magnesium produced by electrolysis of molten salts consists in settling out molten magnesium in a furnace to precipitate impurities in the form of a slime.

At present either crucible electric periodic furnaces or crucibleless continuous electric furnaces are employed in the iron and steel industry for magnesium refining.

A crucible electric furnace has an interior lined with a refractory material and limited by a bottom and side walls. Electric heating elements are fastened to furnace side walls. The furnace is open from above and incorporates an iron or steel crucible with flange resting on the upper furnace end face.

Both the crucible and the furnace are closed at the top with a heat-insulated lid.

Magnesium to be refined is poured into the crucible which is placed in the furnace and closed with the lid. After a certain period slime separates from magnesium and settles on the bottom of the crucible. Next the crucible is removed from the furnace, refined magnesium floating at the top of the melt is decanted, whereupon the slime settled out on the crucible bottom is removed. At the same time another crucible with a new batch of magnesium to be refined is placed into the furnace. However. the productivity of the crubicle electric furnace as determined by the number of crucibles of a given capacity which can be refined in a unit time in the crucible electric furnace does not meet modern requirements. Characteristic of such furnaces is a high specific consumption of electric energy related to a need for heating each crucible with a new portion of magnesium to be refined. and to heavy heat losses which take place when the furnace is open and the crucible is removed therefrom. Peculiar to the crucible furnaces is also a high percentage of oxidation of magnesium. The furnaces require a large number of crucibles and the latter are subject to rapid wear being exposed to heavy weight loads at high temperatures and to oxidation when removed from the furnace.

The maintenance of the crucible furnaces is associated with unfavorable working conditions on account of gases and heat evolved by the melt.

In the prior art, there is an electric crucibleless furnace for continuous magnesium refining, the furnace having a rectangular body comprising a bottom and side walls with a refractory lining. An interior bounded by the side walls and bottom is subdivided by transverse vertical partitions into a number of consecutive chambers. At the level of a magnesium layer each partition is fitted with an opening through which magnesium is capable of overflowing successively from one chamber into another.

At the top the furnace is provided with a roof lined with a refractory material. Above the first chamber the roof has an opening for charging magnesium to be refined, and above the last chamber there is another opening for discharging the refined magnesium. In addition, above each chamber the roof is fitted with slime removal openings closed with covers. Below the level of the openings provided in the partitions all the chambers are filled with molten salt whose specific gravity exceeds that of molten magnesium, e.g., with molten magnesium chloride. To reduce oxidation of magnesium an inert gas is fed into each chamber from above.

The furnace is heated with heat evolved during the passage of electric current through the molten salt or with heat given off by tubular electric heaters introduced into each chamber through the roof.

In such furnaces the refining process is carried on continuously.

Magnesium to be refined is continuously or in separate portions (batchwise) poured through the opening in the roof into the first in the direction of the process flow chamber. Through the openings in the partitions magnesium flows over from one chamber into another with the slime settling out gradually and accumulating in each chamber on the furnace bottom under a layer of molten salt. Magnesium completely freed from impurities is discharged from the last chamber. The slime is periodically discharged from each chamber separately through corresponding openings in the furnace roof.

The above-described continuous furnace is superior in capacity to the periodic crucible furnaces. However, the above furnace does not satisfy as well modern requirements for such furnaces. The crucibleless electric furnace for the continuous refining of magnesium may have an up to 8 m capacity producing up to 40 tons of magnesium per 24 hours with 0.3 weight percent of magnesium being oxidized in the furnace whose service life does not exceed a year. As for the possibility of enhancing the furnace capacity by increasing its dimensions, it is impossible because the furnace partitions wear very rapidly. Usually the partitions between the furnace chambers are produced from a refractory which is subjected to rapid wear under the effect of hydrostatic loads arising due to fluctuations of the melt level in adjoining chambers.

In the course of operation of the furnace considerable difficulties may be encountered.

The slime accumulated during the refining process is removed from each chamber separately. To this end the furnace is shut down and the covers on the slime discharge openings are removed. Both the inert gas and gases, evolving from the melt come out of the furnace through the above openings, contaminating the atmosphere and adversely affecting the working conditions of the attending personnel. At the same time air passes into the furnace through the above openings oxidizing magnesium which settles out together with the slime. Moreover, a considerable amount of heat is removed from the furnace through the above openings. The removal of the slime from the furnace and its subsequent sealing requires a considerable number of attendants and auxiliary equipment. Accordingly, the principal object of the invention is to provide an electric furnace for the continuous refining of magnesium, superior in capacity to the known furnaces.

Another object of the invention is the provision of a furnace featuring high performance characteristics, which would require less electric energy and inert gas in operation and ensure a lower magnesium oxidation percentage owing to the centralized removal of slime.

Still another object of the invention is to proide a reduction in the number of furnace attending personnel and to improve working conditions by decreasing the amount of gases coming out of the furnace.

Yet another no less important object of the present invention is the provision of a furnace having a longer service life resulting from higher durability of partitions and lining.

SUMMARY OF THE INVENTION These and other objects of the invention are achieved by providing an electric furnace for the continuous refining of magnesium with a body lined with a refractory material, and said body comprising walls, a bottom and a roof confining the furnace interior which is subdivided into several chambers by vertical partitions provided with openings for consecutive overflow of magnesium from the first in the direction of the process flow chamber into the next successive ones. The roof has openings for charging magnesium to be refined, discharging the refined magnesium and an opening for slime removal, and is closed with a cover, wherein, according to the invention. the furnace interior is subdivided by the partitions into a central chamber and peripheral ones surrounding it, with the partition limiting the central chamber. The upper section of the partition is closed and butts against the roof at the place of location of the slime removal opening, with the lower end face of the partition being arranged below the level of magnesium within the furnace and spaced apart from the surface of the furnace bottom which is provided with a recess in the form of a basin at a distance exceeding the thickness of a slime layer and enabling the slime to flow off from the peripheral chamber to a bottom section disposed under the central chamber.

The above design of the furnace ensures centralized slime removal and, hence, diminishes magnesium, inert gas and heat losses.

The central chamber accommodates constantly only m'olten salt and not magnesium. Therefore there is no need to interrupt the process when removing the slime from the furnace, since the chambers incorporating magnesium remain closed and air cannot infiltrate therein which precludes magnesium oxidation.

The above-described arrangement of the partitions enables the provision of a furnace design more reliable in service.

Since the lower end face of the central chamber is spaced apart at a preset distance from the furnace bottom, all the chambers communicate with one another in their lower portion which rules out any difference in the melt level within the chambers and, hence, the origination of stresses damaging the partitions. This in turn allows increasing the furnace height and, consequently,

its capacity to -35 m. Such furnaces require less attendants and auxiliary equipment.

It is preferable that the vertical partition bounding the central chanber be made with a ring-shaped crosssection and those bounding the peripheral chambers be disposed radially to the internal surface of the walls of the furnace which is advisable to be made cylindrical in this case.

Due to the above configuration of the central chamber and partition layout, heat losses can be diminished and a more compact furnace construction be provided. Moreover, the radial arrangement of the partitions allows using the cylinder-shaped furnace body which ensures an extended service life of the furnace lining.

The vertical partition limiting the central chamber can be made rectangular in cross-section and disposed coaxially with the walls of the furnace which is advisable to be made right-angled on this occasion.

This facilitates the laying of the lining in the furnaces in the small capacity range.

BRIEF DESCRIPTION OF THE DRAWINGS The present invention will be better understood from a consideration of a detailed description of an examplary embodiment thereof, to be had in conjuction with the accompanying drawings, wherein:

FIG. 1 shows a furnace, according to the invention, in cross section taken along a vertical plane passing through the longitudinal axis of the furnace;

FIG. 2 is a sectional view taken along the line 22 of FIG. 1;

FIG. 3 is a top view of an alternate furnace with its roof removed, and illustrating the furnaces rectangular body and central chamber;

FIG. 4 is a top view, similar to FIG. 3, but of another alternate furnace with a rectangular body and cylindri cal central chamber; and

FIG. 5 is a top view,similar to FIGS. 3 and 4, but of yet another alternate furnace with elliptical body and a rectangular central chamber.

DESCRIPTION OF THE PREFERRED EMBODIMENTS As best shown in FIGS. 1 and 2, there is illustated an electric furnace for the continuous refining of magnesium, comprising a hollow cylindrical body 1 with a refractory lining 1. A furnace bottom 3 has a recess in its central portion in the form of a basin 4. At the top the furnace is provided with a roof 5 which has the following openings: an opening 6 for charging magnesium to be refined; and opening 7 for discharging the refined magnesium; and an opening 8 for the removal of slime, the opening being closed with a cover 9.

According to the invention, adjacent to the roof 5 at the place of the opening 8 is an upper portion of a closed partition limiting a central chamber 10. The lower end face of the partition of the chamber 10 is located below the level of a magnesium layer 11 and is spaced apart from the furnace bottom 3 at a distance exceeding the thickness of a layer of slime l2 accumulating in the basin 4.

Arranged intermediate of the brick-lined body 1 and the central chamber 10 are a plurality of radial partitions 13 with openings 14 for the overflowing of magnesium in the direction of the process flow (shown by the reference arrows in FIG. 2) from a first peripheral chamber 15 into the next successive ones. The partition 16 separating first chamber 15 from the last chamber 18 has no opening. The remaining radial partitions 13 form other peripheral chambers 17 and 18.

The opening 6 in the roofS is disposed above the chamber 15, the magnesium discharge opening 7 being located in the same roof 5 above the chamber 18. No

openings are provided in the roof above the chamber 17. As the lower end face of the partition of the cham ber 10 does not reach the furnace bottom 3, the lower portion of all the peripheral chambers 15, 17 and 18 are in communication with one another.

The furnace is furnished with electrodes 19 for the passage of electric current and when the latter passes through a salt layer 20, heat is evolved. The furnace right-angledtsquare or rectangular central chamber 23 with the furnace body 24 being rectangular (FIG. 4) or elliptical 25 (FIG. 5).

The furnace operates in the following manner.

Before the process is initiated the furnace is filled with the molten salt 20 having a higher specific gravity than the molten magnesium l1, e.g., molten magnesium chloride or a mixture of magnesium, potassium and sodium chlorides. Next an inert gas is supplied into the furnace through the connecting pipe 22 and electric current is passed to the electrodes 19 and/or tubular heaters 21. After the furnace has been adequately heated, the process of magnesium refining is initiated.

The molten magnesium 11 to be refined is charged into the chamber 15 through the opening 6 in the roof 5 continually or in separate portions, with the level of the molten salt 20 in the chambers l5, l7 and 18 diminishing and within the chamber 10 rising. The magnesium ll overflows from the chamber through the opening 14 into the chamber 17 and then into the chamber 18. Magnesium impurities settle out gradually in the form of a slime 12 passing through the layer of the salt and precipitating in the basin 4 on the furnace bottom 3. Refined magnesium is discharged from the chamber 10 through the opening 7 in the roof 5.

The magnesium 11 does not enter the chamber 10 which incorporate always only the molten salt 20.

The slime 12 is removed from the furnace at regular intervals as it accumulates therein. To this end upon removing the cover 9 form the opening 8 in the roof 5, one penetrates through the chamber 10 under the salt layer 20 to the layer of slime collected in the basin 4. In this case the peripheral chambers 15, 17 and 18 remain sealed, the magnesium refining process proceeding therein.

Tests of the hereinbefore-described furnace have shown that all the slime l2 precipitating from the molten magnesium 11 in the peripheral chambers l5, l7 and 18 runs off to the center of the furnace bottom 3 into the basin 4 disposed under the central chamber 10.

The removal of the slime 12 from the furnace does not necessitate any interruptions in the refining process. During the removal of the slime 12, the peripheral chambers of the furnace remain sealed and air does not infiltrate therein which would reduce substantially the oxidation of magnesium and the consumption of inert gas.

Since only one opening of the furnace was open and the slime was removed only form a single place, heat losses could be decreased, working conditions improved and the number of attendants decreased.

The use of central and peripheral chambers and an efficient arrangement of partitions enabled the provision of a furnace with an annular cross-section which leads to a reduction in the external surface of the furnace and. hence, in heat losses. The annular crosssection of the furnace contributes to an enhanced durability of the furnace body and lining. All the peripheral chambers of the furnace communicate with one another in their lower portion, the melt level in the chambers being thereby always the same and the partitions separating the chambers being not exposed to periodic hydrostatic loads by which virtue their durability is equal to that of the furnace lining.

Such a furnace of a 30-35 m capacity has an efficiency of -100 tons per 24 hrs, its service life amounting to no less than 2 years; and oxidation of magnesium in the furnace does not exceed 0.1 weight percent.

Although the present invention has been described in some detail by way of illustration and example for purposes of clarity of understanding, it will, of course, be understood that various changes and modifications may be made in the form, details, and arrangment of the parts without departing from the scope of the invention as set forth in the claims.

What we claim is:

l. A furnace for the refining of a metal. such as magnesium and the like having a refractory lined bottom, side walls and a roof and comprising: vertically disposed partition means dividing said furnace into a centrally disposed chamber and a plurality of chambers disposed peripherally about said central chamber, said central chamber having removable cover means, and being'sealed with respect to said peripheral chambers by means of a molten salt mass when said furnace is in operation; all of said chambers communicating with each other at their lower portions; each of said peripheral chambers communicating with an adjacent peripheral chamber at a level in said furnace so as to ensure the consecutive overflow of refined metal from a first peripheral chamber to a last peripheral chamber, and opening means in said roof for charging said furnace and for discharging said refined metal.

2. The furnace according to claim 2, wherein said vertically disposed partition means includes a plurality of radially disposed partitions extending radially between the side walls of said furnace and said vertically disposed partition means defining said centrally disposed chamber.

3. The furnace according to claim 2, wherein said centrally disposed chamber is circular in cross-section.

4. The furnace according to claim 3, wherein said furnace is cylindrical in shape.

5. The furnace according to claim 3, wherein said furnace is square in shape.

6. The furnace according to claim 2, wherein said centrally disposed chamber is square in cross-section.

7. The furnace according to claim 6, wherein said furnace is square in shape.

8. The furnace according to claim 6, wherein said furnace is cylindrical in shape.

3. The furnace according to claim 2, wherein said centrally disposed chamber is rectangular in crosssection.

10. The furnace according to claim 1, wherein said furnace is elliptical in shape.

11. The furnace according to claim 1, wherein said furnace is of the electric type.

12. The furnace according to claim 1 including at least one electrode for each of said peripheral chambers.

13. The furnace according to claim 12, including at least one tubular electric heater in at least said first peripheral chamber.

14. In the method for refining magnesium in a furnace, wherein molten magnesium is maintained above a layer of molten salt having a density greater than that of the molten magnesium, at a temperature and for a period of time sufficient to precipitate. as a slime. impurities from the molten magnesium. the precipitated slime having a density greater than that of the molten salt, the slime collecting below the level of the molten salt, the improvement comprising: passing the molten magnesium through a plurality of successively interconnected treatment chambers. the treatment chambers being interconnected at an upper level to permit passage of molten magnesium and at a bottom level to permit passage of molten salt and precipitated slime;

passing the precipitated slime from the lower portions of each of the successively interconnected chambers to an elimination chamber sealed out of contact with the molten magnesium but being interconnected at the bottom level to the layer of molten salt in the treatment chambers the bottom level of the elimination chamber being vertically below the bottom level of the treatment chambers; and removing the precipitated slime from the elimination chamber; whereby precipitated slime from the treatment chambers collects in the elimination chamber from which it is eliminated without exposing the molten magnesium to the atmosphere. 

1. A FURBACE FOR THE REFINING OF METAL, SUCH AS MAGNESIUM AND THE LIKE HAVING A REFRACTORY LINED BOTTOM, SIDE WALLS AND AROOF AND COMPRISING: VERTICALLY DISPOSED PARTITION MEANS DIVIDING SAID FURNACE INTO A CENTRALLY DISPOSED CHAMBER AND A PLURALITY OF CHAMBERS DISPOSED PERIPHERALLY ABOUT SAID CENTRAL CHAMBER, SAID CENTRAL CHAMBER HAVING REMOVABLE COVER MEANS, AND BEING SEALED WITH RESPECT TO SAID PERIPHERAL CHAMBERS BY MEANS OF A MOLTEN SALT MASS WHEN SAID FURNACE IS IN OPERATION; ALL OF SAID CHAMBERS CIOMMUNICATING WITH EACH OTHER AT THEIR LOWER PORTIONS; EACH OF SAID PERIPHERAL CHAMBERS COMMUNICATING WITH AN ADJACENT PERIPHERAL CHAMBER AT A LEVEL IN SAID FURNACE SO AS TO ENSURE THE CONSECUTIVE OVERFLOW OF REFINES METAL FROM A FIRST PERIPHERAL CHAMBER TO ALAST PERIPHERAL CHAMBER, AND OPENING MEANS IN SAID ROOF FOR CHARGING SAID FURNACE ANDFOR DISCHARGING SAID REFINED METAL.
 2. The furnace according to claim 2, wherein said vertically disposed partition means includes a plurality of radially disposed partitions extending radially between the side walls of said furnace and said vertically disposed partition means defining said centrally disposed chamber.
 3. The furnace according to claim 2, wherein said centrally disposed chamber is circular in cross-section.
 4. The furnace according to claim 3, wherein said furnace is cylindrical in shape.
 5. The furnace according to claim 3, wherein said furnace is square in shape.
 6. The furnace according to claim 2, wherein said centrally disposed chamber is square in cross-section.
 7. The furnace according to claim 6, wherein said furnace is square in shape.
 8. The furnace according to claim 6, wherein said furnace is cylindrical in shape.
 9. The furnace according to claim 2, wherein said centrally disposed chamber is rectangular in cross-section.
 10. The furnace according to claim 1, wherein said furnace is elliptical in shape.
 11. The furnace according to claim 1, wherein said furnace is of the electric type.
 12. The furnace according to claim 1 including at least one electrode for each of said peripheral chambers.
 13. The furnace according to claim 12, including at least one tubular electric heater in at least said first peripheral chamber.
 14. In the method for refining magnesium in a furnace, wherein molten magnesium is maintained above a layer of molten salt having a density greater than that of the molten magnesium, at a temperature and for a period of time sufficient to precipitate, as a slime, impurities from the molten magnesium, the precipitated slime having a density greater than that of the molten salt, the slime collecting below the level of the molten salt, the improvement comprising: passing the molten magnesium through a plurality of successively interconnected treatment chambers, the treatment chambers being interconnected at an upper level to permit passage of molten magnesium and at a bottom level to permit passage of molten salt and precipitated slime; passing the precipitated slime from the lower portions of each of the successively interconnected chambers to an elimination chamber sealed out of contact with the molten magnesium but being interconnected at the bottom level to the layer of molten salt in the treatment chambers, the bottom level of the elimination chamber being vertically below the bottom level of the treatment chambers; and removing the precipitated slime from the elimination chamber; whereby precipitated slime from the treatment chambers collects in the elimination chamber from which it is eliminated without exposing the molten magnesium to the atmosphere. 